Cell growth and division in eukaryotic organisms is mediated through the cell cycle. The cell cycle consists of two major events separated by two central gap phases. DNA synthesis and replication occur during the S phase while mitosis occurs during the M phase. A first gap phase, called G.sub.1, which occurs between the M phase and the S phase, allows for accumulation of enzymes and other compounds necessary to drive DNA synthesis and genome replication. A second gap phase, called G.sub.2, occurs between the S phase and the M phase, allowing for controls to check for proper DNA replication prior to committing to cell division. Transition to and passage through the four stages of the eukaryotic cell cycle are regulated by a family of cyclin-dependent protein kinases (CDKs). Activation of a CDK requires binding to a cyclin regulatory subunit, and in the case of CDK1-CDK6, phosophorylation of threonine 160/161 (Thr160/161). These CDKs contain a cyclin binding site near the amino terminal portion of the protein. The activated CDK/cyclin complex phosphorylates proteins involved in various stages of the cell cycle.
The family of cyclin proteins may generally be classified as either G.sub.1 cyclins or mitotic cyclins, depending on peak expression levels. A CDK may bind a subset of cyclins. For example, CDK4 is known to bind cyclin D1 or cyclin D3 whereas CDK2 is known to bind cyclin A, cyclin B1, cyclin B2, cyclin B3 and cyclin E. The vertebrate cyclins show homology within a region of approximately 100 amino acids, referred to as the cyclin box. This region is responsible for CDK binding and activity (Kobayashi, et al., 1992, Molec. Biol. Cell. 3: 1279-1294; Lees, et al., 1993, Molec. Cell. Biol., 1993, 13: 1194-1201). It is this region of the cyclin protein which interacts with the cyclin binding domain of a respective CDK protein.
Complete activation of a known CDK/cyclin complex requires phosphorlyation by a CDK-Activating Kinase (CAK). The vertebrate CAK has been identified as a CDK/cyclin complex, more specifically CDK7/cyclinH (Fisher and Morgan, 1994, Cell 78: 713-724). The CAK enzyme comprises a threonine 170 residue (in human CDK7) which has been shown to be required for optimal activity (Poon, et al., 1994, J. Cell Sci. 107: 2789-2799; Fisher and Morgan, 1994, Cell 78: 713-724).
Inhibition of CDK/cyclin complexes are thought to occur via phosphorylation at threonine 14 (Thr14) and/or tyrosine 15 (Tyr15) of the CDK subunit. The Weel kinase has been suggested as either a Thr14 kinase or as a Thr14 and Tyr15 kinase. Additionally, CDC25 is thought to be a dual kinase targeting both Thr14 and/or Tyr15 (Morgan, 1995, Nature 374: 131-134).
It would be advantageous to identify a gene encoding an additional CDK protein. A nucleic acid molecule expressing a CDK protein would be extremely useful in screening for compounds acting as a modulator of the cell cycle. Such a compound or compounds will be useful in controlling cell growth associated with cancer or immune cell proliferation. Additionally, the recombinant form of protein expressed from such a novel gene would be useful for an in vitro assay to determine specificity toward substrate proteins, inhibitors and cyclin activators. Additionally, an isolated and purified CDK10 cDNA which encodes CDK-10 or an active mutant thereof will also be useful for the recombinant production of large quantities of respective protein. The ability to produce large quantities of the protein would be useful for the production of a therapeutic agent comprising the CDK10 protein or a mutant such as the exemplified mutant disclosed herein. A therapeutic agent comprised of CDK10 protein would be useful in the treatment of cell cycle and/or CDK10 related diseases or conditions which are CDK10 responsive. The present invention addresses and meets this need.